jan: yes its not a typical current output DAC, but 780Ω isnt that unmanageable and its not like the Ti 179X chips are ideal current sources, its when people parallel them for dual mono and fail to take into account that this lowers each mono output less than 100Ω. All this effort and expense undertaken while not getting any better performance than what you can get with a single one. These people seem not to notice that the chip is built from the ground up, with convenient pinout and internal fully isolated L/R channels, so as long as your layout and power supply is dual mono, you have a dual mono dac. of course without 2 or more chips its not fashionably dual mono

My guess is that they did the lowish Zout precisely to be able to parallel outputs just like that and reap some benefits from it.

Interestingly, while Oppo did that in earlier models (and switch the whole parallel bunch into whatever analog output was used at any moment), in the newer 105 they just use the separate outputs to feed all analog outs permanently.
I wonder why (but realise that cheaper implementation may have something to do with that).

Not saying the Oppo 105 isn't a great machine - it is for me.
But that, of course, comes from a myriad of other factors, which you can't all improve just with a different I/V opamp.

My guess is that they did the lowish Zout precisely to be able to parallel outputs just like that and reap some benefits from it.

its difficult enough to make the ENOB for a single ESS chip laid out as stereo balanced (4 parallel a channel, standard implementation with 195Ω Zout). given its fully dual mono already and using 2 you will still have the same difficulty making them count, plus more current to deal with ... i'm not sure the reasons are there on a purely engineering standpoint.

it has perhaps some marginal benefits for power supply layout and potential sales only IMO. there is more to be gained by spending some money on an FPGA for tweaking the internal digital filters/registers and clocking, but that does require some significant investment in staff.

Quote:

Not saying the Oppo 105 isn't a great machine - it is for me.
But that, of course, comes from a myriad of other factors, which you can't all improve just with a different I/V opamp.

jan

just a different opamp? that by itself would be futile. I didnt suggest just a different opamp, almost nothing I mentioned above was done and I only scratched the surface, space and of course probably lack of interest in the audience here for my own recommendations are likely low enough.

when I was talking about monolithic duals and fets above, i'm not talking about opamps, i'm talking about dual or quad monolithic mosfets or dual monolithic bipolar transistors for the input stage, followed by a fully differential opamp as a composite opamp, but I touched on a few other areas that were seemingly ignored as well.

i'm sure it does its job quite well regardless and as you say there is more to this equation given its purpose, the ES9018 seems to be capable of pretty good performance even with suboptimal implementation, but it certainly presents some opportunities to get the best out of it.

A brute force approach can also be done. Drop a small resistor across the summing junction and parallel a bunch of active devices to amplify. Not really any more trouble than getting similar current levels to drive feedback resistors.

All good fortune,
Chris

Or drop a big cap right across the output and make a critically damped two pole TIA with a low noise VFA and suitable feedback cap. Now when the op-amp output impedance goes up a RF frequencies there is a cap right at the input to take over.

__________________
"The question of who is right and who is wrong has seemed to me always too small to be worth a moment's thought, while the question of what is right and what is wrong has seemed all-important."

Others may disagree here, but I feel lowest noise is more important than low impedance or ultra-wide bandwidth for reference and clock supplies, as long as local decoupling is up to snuff; certainly if you are budget and space constrained.

I like your thinking, qusp - to me, every pin or link going into the DAC is a potential troublemaker, I would be absolutely paranoid about trying to optimise each connection here.

For me, the killer of digital sound has always been interference effects - even the roughest, standard, D/A section has put up a good show if I baby it really, really carefully ...